Epigenetic changes, particularly alterations in DMAmethylation, contribute to oncogenesis in at least two respects. First, overall DMA methylation is reduced in tumors, which leads to aberrant gene activation and genomic instability. Second, CpG island promoters become hypermethylated, which leads to transcriptional silencing and the functional inactivation of tumor suppressor genes. In addition to changes in DNA methylation, other important epigenetic changes have been observed in human cancer, including alterations in histone modification patterns and histone modifying enzymes. Our long-term objective is to understand the molecular mechanisms that initiate and maintain abnormal epigenetic states in human cancer. To meet this objective, we are utilizing cancer/germ-line (CG) antigen genes as models. CG antigens are an intriguing gene family whose aberrant expression in human cancer appears to result from epigenetic deregulation. In addition, CG antigens are HLA-restricted tumor antigens that trigger humoral and cell- mediated immune responses in cancer patients; CG antigen directed vaccines are currently in numerous human clinical trials. Thus, in addition to serving as a model for understanding epigenetic deregulation in cancer, CG antigens are clinically relevant. We hypothesize that CG antigen gene expression is epigenetically regulated by the action of specific DNA methyltransferases (DNMTs) and histone methyltransferases. To test this hypothesis, we will pursue four complementary and unified specific aims: 1) Determine the mechanism by which DNMTs repress CG antigen gene expression in human cancer cells; 2) Define the histone H3 tail lysine modifications that control CG antigen gene expression in human cancer cells; 3) Ascertain the role of the histone methyltransferases G9a and Eu-HMTasel in CG antigen gene regulation in human cancer cells; and 4) Determine whether NY-ESO-1 expression is associated with DNA hypomethylation in epithelial ovarian cancer. This study will impact public health by improving our understanding of why only certain patients express clinically important cancer vaccine targets. Furthermore, this study will provide key information relevant for understanding the outcome and improving the future design of clinical vaccine trials for the treatment of ovarian cancer.